Subsoil properties and cereal growth as affected by a single pass of heavy machinery and two tillage systems on a Luvisol

Compared to moldboard plowing, conservation tillage is frequently discussed to alleviate soil stresses caused by high wheel loads and, thus, decrease the risk of subsoil compaction. On a Luvisol derived from loess (Gottingen, Lower Saxony, Germany), a wheeling experiment was conducted in two contrasting tillage systems (continuous moldboard plowing [MP] 30 cm deep and shallow mixing [SM] 10 cm deep). A six-row self-propelled sugar beet tanker harvester (SBH 6: 34–36 Mg total vehicle weight, 8–11 Mg wheel load, 92–143 kPa calculated ground-contact pressure) was used for a single pass. Each crop of the sugar beet–cereal–cereal rotation was cultivated with light experimental machinery on one of three adjacent fields each year. In October 2001 (Field 2), 2002 (Field 1), and 2003 (Field 3) wheeling with the SBH 6 was carried out on half of every tillage plot (soil moisture 70%–100% field capacity) after the harvest of previous sugar beet. Subsequently, the soil was tilled according to the respective treatment, and winter wheat, spring wheat, and spring barley were grown on Field 2, 1, and 3, respectively. During the following spring and summer, soil and plant measurements were conducted. Soil penetration resistance (10–25 cm) increased, and root length density of spring wheat decreased in SM tillage compared to MP tillage. At 40–45 cm depth, air-filled pore volume at 6.2 kPa water tension (two fields), air permeability, and total pore volume (one field) were higher in SM than in MP treatments, respectively. Wheeling slightly increased penetration resistance in 15–25 cm depth but had no effect on any parameter measured at 40–45 cm soil depth. Generally, treatment effects on cereal-grain yield were small and insignificant. Our results suggest that a single pass with a SBH 6 is unlikely to cause pronounced subsoil-structure degradation on a loessial soil under moderate climatic conditions.